This invention relates to a method and apparatus for drying a workpiece such as a substrate used in magnetic disk or integrated circuit manufacturing.
In many manufacturing processes it is necessary to treat a workpiece with a liquid and then dry the workpiece. For example, during the manufacturing of magnetic disks, one typically performs the following manufacturing steps:
1. First, a nickel-phosphorus layer is plated onto an aluminum substrate;
2. The nickel-phosphorus layer is polished and textured;
3. The substrate is cleaned, rinsed and dried;
4. A series of layers are sputtered onto the substrate, e.g. an underlayer such as sputtered NiP or Cr, a magnetic cobalt alloy, and a protective hydrogenated carbon overcoat. An example of such a process is described in U.S. Pat. No. 6,150,015, issued to Bertero et al. and incorporated herein by reference.
Immediately prior to sputtering, the substrate is cleaned and then dried. It is very important that when the substrate is dried, there should be no impurities left on its surface.
Numerous other manufacturing processes require drying a workpiece. For example, during various semiconductor manufacturing process steps, semiconductor wafers are immersed in a liquid and then dried. It is very important that there be no impurities on the surface of these wafers after drying.
One apparatus for drying semiconductor wafers is discussed in European Patent Application 0 385 536. In the ""536 apparatus, a wafer is immersed in a liquid and then slowly removed from the liquid in the presence of a vapor that aids in the drying process. The cooperation of this vapor and liquid creates the so-called Marangoni effect, which facilitates drying of the wafer. In the ""536 apparatus, a xe2x80x9cknife-shaped memberxe2x80x9d pushes the wafer out of a liquid and into a region where the wafer can be dried.
Another apparatus for drying semiconductor wafers is discussed in U.S. Pat. No. 5,569,330, issued to Schild et al. Schild also teaches a structure that pushes a wafer out of a liquid into a region where the wafer can dry.
During some prior art drying processes, a wafer is held by a holding structure while it is drying. This leaves the possibility of some contamination or drying marks at the point where the drying wafer is held by the holding structure. One apparatus for dealing with this problem is discussed in U.S. Pat. No. 5,884,640, issued to Fishkin et al. In Fishkin""s drying apparatus, instead of pushing a wafer out of a liquid-containing bath, the liquid is drained from the bath. As the liquid level falls with respect to the wafer, the wafer is held at different points so that portions of the wafer are not in mechanical contact with a holding structure while those portions are drying.
U.S. Pat. No. 4,722,752, issued to Steck, discusses another apparatus for drying wafers. Steck""s apparatus contains two support structures capable of lifting wafers out of contact with a liquid. A first structure (comprising bars 34 in Steck FIG. 5) lifts Steck""s wafers 24 partially out of contact with a liquid. During this time period, a cassette 25 is immersed in the liquid. Steck then pushes cassette 25 out of his liquid. Eventually, cassette 25 dries and thereafter comes into contact with a dry portion of wafers 24. Steck must allow enough time between the time cassette 25 leaves contact with the liquid and the time cassette 25 contacts wafers 24 so that cassette 25 can dry. This potentially limits the throughput of Steck""s device.
A method for drying a workpiece in accordance with the present invention comprises lifting the workpiece out of a liquid bath with a first holding structure until a first portion of the workpiece extends out of the liquid. (At this point in the process, a second portion of the workpiece remains within the liquid.) During this part of the method, the first holding structure is immersed in the liquid, and the portion of the workpiece where the first holding structure contacts the workpiece is immersed in the liquid. The portion of the workpiece extending out of the liquid dries. A second holding structure grabs the dry portion of the workpiece extending out of the liquid, and thereafter lifts the workpiece out of contact with the first holding structure and out of contact with the liquid. (The portion of the second holding structure that lifts the workpiece is dry, and typically, this portion of the second holding structure is never immersed within the liquid. In one embodiment, no portion of the second holding structure is immersed within the liquid.) The second portion of the workpiece then dries. In one embodiment, at no time is a drying portion of the workpiece in contact with a holding structure. Thus, the chance of creating drying marks or contamination on the workpiece is minimized.
Another advantage of a method in accordance with the invention is that because the second holding structure is never immersed in the liquid, there is no need to wait until the second holding structure dries before it can grab the workpiece. Thus, a method in accordance with the invention is expected to be more efficient than the above-described Steck method.
In one embodiment, the workpiece is a substrate used to manufacture a magnetic disk. The workpiece can be a nickel-phosphorus plated aluminum alloy, glass, glass ceramic, or other material. After drying, various layers such as an underlayer, a magnetic layer, and a protective layer are deposited (e.g. by sputtering, CVD, PECVD, or other technique) onto the workpiece. However, the workpiece can be another type of structure as well, e.g. a semiconductor wafer.
In one embodiment, several (or many) workpieces are dried simultaneously.
In one embodiment, the workpiece is raised at a first speed during the time that the top of the workpiece breaks the surface of the liquid. The workpiece is raised at a second speed after the top of the workpiece has broken the surface of the liquid. The first speed is slower than the second speed. Also, in one embodiment, the workpiece is raised at a third speed during the time when the bottom of the workpiece breaks the surface of the liquid. The third speed is slower than the second speed. The reason for this is that different portions of the workpiece dry at different rates. By adjusting the speed with which the workpiece is raised to accommodate the drying rate of the different portions of the substrate, the overall speed with which the workpiece is dried is improved.
The workpiece can be a substrate having a centrally defined opening. In such an embodiment, the workpiece is raised at a fourth speed during the time the top of the centrally defined opening breaks the liquid surface and the time the bottom of the centrally defined opening breaks the liquid surface. The fourth speed is typically slower than the second speed for reasons stated above. The substrate is raised at a fifth speed after the top of the centrally defined opening breaks the liquid surface but before the bottom of the centrally defined opening breaks the liquid surface. The fifth speed is typically greater than the fourth speed. Optionally, the fifth and second speeds can be equal. The first, third and fourth speeds can also be equal. As mentioned above, the speed with which the substrate is raised is modified to account for the fact that the substrate dries more slowly during the time that the top and bottom of the substrate and the top and bottom of the centrally defined opening break the surface of the liquid.
In one embodiment, a gas or vapor is provided above the top surface of the liquid to facilitate drying. In one embodiment, this vapor comprises IPA (isopropyl alcohol), but other materials can be used, e.g. acetone. Thus, an embodiment of the invention can employ the above-mentioned Marangoni effect.